1. Field of the Invention
This invention relates to an interface circuit suitable for use with an automated test station of the type in which a test control unit sends stimulus information to a unit under test (UUT), samples responses from the UUT, and analyzes the responses to determine whether the UUT is good or faulty, and more particularly to an interface circuit which generates additional response channels from the response channels provided by the test control unit, thereby expanding the response channel count.
2. Description of Related Art
As high technology systems, such as avionics or weapons systems, become increasingly reliant upon sophisticated electronic or electromechanical components, the number and complexity of test procedures required to provide support for the systems also increases.
A variety of automated test systems have been developed which enable implementation of a large number of relatively complex test procedures without substantially increasing the level of skill and time required to operate the systems. These systems have in common the ability to send stimulus information to the UUT, and to sample and analyze responses from the UUT.
For example, the Hewlett-Packard Corporation currently manufactures a system known as the HP16500 Logic Analysis System (LAS) designed to apply stimuli to the UUT using a stimulus sub-system, the responses being stored in a response sub-system and then compared to the expected responses generated by a software simulation tool to determine whether the UUT is good or faulty. Both the stimulus and response sub-systems are conveniently contained in a single unit for use in an integrated automated test station. The number of response channels available when using a single test control unit such as HP16500 is dependent on the configuration of stimulus and response circuit cards in the unit's card cage. An optimal balance of stimulus and response channels in the HP16500, for example, is achieved by fully populating the card cage with three stimulus cards and two response cards. This configuration provides 160 response channels.
It is not uncommon, however, for state-of-the-art UUTs to require more response channels than is provided by the HP16500 and other conventional test control units. While the channel count can be increased by adding another discrete test control unit to the system, this is impractical for reasons of cost and size, and also because of the software complications involved in simultaneous control of the two units. As a result, it would be desirable to provide a channel expander arrangement which can be used with, or retrofitted onto, an existing unit in order to enable the existing unit to accommodate UUTs with increased channel requirements but without requiring significant modification of the existing unit. No such channel expander arrangement is currently available.